How sensitive are trace gas concentrations to the method used to parameterize clouds within CMAQ?

1. How sensitive are trace gas concentrations to the method used to parameterize clouds within CMAQ? Christopher P. Loughner1, Dale J. Allen1, Russell R. Dickerson1, Kenneth E. Pickering1,2, Yi-Xuan Shou3, and Da-Lin Zhang1 1Department of Atmospheric and Oceanic Science, University of Maryland, College Park, MD 2NASA Goddard Space Flight Center, Greenbelt, MD 3National Satellite Meteorological Center, China Meteorological Administration, Beijing, China CMAS Conference October 12, 2010

2. Introduction • Investigate the influence of grid resolution on fair-weather cumulus clouds and sulfur dioxide oxidation. • Examine the differences in the cloud parameters used in CMAQ’s photolysis and aqueous chemistry schemes and determine the sensitivity of sulfate to cloud representation. • Investigate the influence of grid resolution on the Chesapeake Bay breeze, the dispersion of pollutants, and ozone formation.

3. Background • SO2 oxidation in clouds: • CMAQ and GOCART over-predict SO2 column content by approximately 50% over the Eastern US, which is possibly due to an underestimation of SO2 oxidation in clouds (Hains, 2007). • Mueller et al. (2006) noted CMAQ has a low cloud bias and used alternative cloud parameterizations, which improved the frequency of clear sky and overcast conditions but not partly cloudy sky conditions. • Mueller et al. (2006) also noted CMAQ may underestimate the removal of pollutants from the PBL through convective venting. • Sea (bay) breeze and ozone concentrations: • Peak ozone concentrations occur at the furthest inland location of a sea breeze’s convergence zone (Boucouvala and Bornstein, 2003) • CMAQ better simulates ozone in the presence of a sea breeze at 2km resolution than 4 or 8km (Jimenez et al., 2006). Boucouvala, D. and R. Bornstein (2003), Analysis and transport patterns during an SCOS97-NARSTO episode, Atmos. Environ., 37, #2 S73-S94. Hains, J.C. (2007), A chemical climatology of lower tropospheric trace gases and aerosols over the Mid-Atlantic region, Ph.D. Thesis, Department of Atmospheric and Oceanic Science, University of Maryland, College Park, MD, pp. 254. Jimenez, P., O. Jorba, R. Parra, and J.M. Baldasano (2006), Evaluation of MM5-EMICAT2000-CMAQ performance and sensitivity in complex terrain: High-resolution application to northeastern Iberian Peninsula, Atmos. Environ., 40, 5056-5072. Mueller, S.F., E.M. Bailey, T.M. Cook, Q. Mao, 2006: Treatment of clouds and the associated response of atmospheric sulfur in the Community Multiscale Air Quality (CMAQ) modeling system, Atmos. Environ., 40, 6804-6820.

4. Method • WRF-Urban Canopy Model and CMAQ simulations are analyzed with four nested domains at 13.5, 4.5, 1.5, and 0.5km horizontal resolution for a base case and a sensitivity case with altered clouds. • Time period: 12 UTC July 7, 2007 to 12 UTC July 10, 2007 plus 2 week spin-up for domain 1. On July 7 fair-weather cumulus clouds were present and on July 9 8-h max ozone reached 125ppb in northeastern MD. • Meteorological initial and boundary conditions: North American Regional Reanalysis • Chemical initial and boundary conditions: MOZART CTM (Louisa Emmons, NCAR) • Emissions: Processed with SMOKE with projected 2009 emissions from the US Regional Planning Offices and 2007 Continuous Emissions Monitoring data.

5. Models

6. Model updates • For base and sensitivity cases: • MCIP: Write out the percentage of urban area of each grid cell for a WRF-UCM simulation (available in Version 3.5_beta and beyond) • MCIP: Set CO dry deposition velocity to 0.0 cm s-1 (Castellanos, 2009) • CMAQ: Set minimum eddy diffusion coefficient to 0.1 m2 s-1 (Castellanos, 2009) • CMAQ: Implemented bug fixes for advection and horizontal diffusion schemes (T. Odman and Y. Hu, unpublished, available at http://people.ce.gatech.edu/~todman/bugs/bugs.htm) • For sensitivity case: • MCIP: Calculate 3-dimensional aqueous chemistry cloud properties using same algorithm used to calculate 2-dimensional photolysis scheme cloud properties Castellanos, P. (2009), Analysis of temporal sensitivities and vertical mixing in CMAQ, and measurements of NO2 with cavity ring-down spectroscopy, Ph.D. Thesis, Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, MD, pp. 165.

7. GOES visible satellite image and average cloud liquid water content from the 13.5 and 0.5km base case simulations at 2000 UTC (3pm EST) July 7, 2007. 13.5km 0.5km

8. 13.5km GOES visible satellite image and average cloud liquid water content from the 13.5 and 0.5km sensitivity simulations at 2000 UTC July 7, 2007. 0.5km

9. Average cloud fraction and cloud liquid water content averaged over the inner-most domain. Base Case Sensitivity Case

10. SO4 cross-sections averaged over inner-most domain at 2000 UTC July 7, 2007. Base Case Sensitivity Case 13.5km 0.5km

11. SO2 observations and base case model results at Beltsville, MD and Essex, MD. High bias in SO2 possibly due to large spatial variability.

12. Surface to 215mb SO2 column at 1200 UTC July 8, 2007 averaged over the inner-most domain. • 0.5km base case SO2 column 23% smaller than 13.5km base case. • 0.5km base case has a net flux of 70% more total sulfur out of the area of the innermost domain than the 13.5km base case. • 0.5km sensitivity case SO2 column 38% smaller than 13.5km base case.

13. 24-h average SO4 observations and model results on July 8, 2007 at Washington, DC.

14. WRF-UCM 2-m temperature and 10-m wind speed at 2000 UTC (3pm EST) July 9, 2007. A stronger temperature gradient along the coastline of the Chesapeake Bay in the 0.5km domain results in a stronger Bay breeze. 13.5km 0.5km

15. Cross-section of CO between Washington, DC and Baltimore, MD for the 13.5 and 0.5km simulations. The stronger bay breeze in the 0.5km simulation causes higher pollutant concentrations at the bay breeze convergence zone where they are lofted and then transported downwind. coastline coastline 13.5km 0.5km

16. 8-hr max O3 concentrations on July 9, 2007 from measurements and the base case simulation. Less pollutants over the water in the higher resolution simulations due to a stronger bay breeze results in lower ozone concentrations over the water.

17. Conclusions • Higher resolution simulations result in more sulfur dioxide oxidized to sulfate aerosols in the presence of fair-weather cumulus clouds. • Higher resolution simulations cause more pollutants to be vented from the PBL to the free troposphere. • Inconsistencies between the cloud properties used in CMAQ’s aqueous chemistry and photolysis schemes were examined. For this particular case the photolysis cloud properties better agrees with satellite observations. • The sensitivity case resulted in more SO2 oxidized to SO4 due to more fair-weather cumulus clouds present showing the importance of fair-weather cumulus clouds to the sulfur budget. • Higher resolution simulations result in a stronger bay breeze. • A stronger bay breeze prevents pollutants from being transported near the surface from land to water resulting in lower near surface ozone concentrations over the water and higher ozone concentrations near the bay breeze convergence zone.